The present invention is generally directed to a springless pilot operated sequence valve providing a two-position, three-way valve which is particularly useful for controlling a plurality of underwater devices.
As disclosed in U.S. Pat. No. 3,999,100, sequence valves are used in production control system applications for underwater gas and/or oil wells in which a plurality of sequence valves operate in sequence to control multiple tree valves and subsurface safety valves using only a single pilot or signal control line. That is, the functions are operated in a specific sequence, generally by increasing pressure increments on the pilot line for opening a production well. During the process of closing in the well, all of the production valves are closed, generally in the reverse order, by decreasing the pilot pressure in decreased pressure increments. However, currently used sequence valve designs utilize springs. Such springs are under a constant state of compression and over a long period of time the springs lose some of their load capability which changes the operating characteristics of the valve. In addition, while it is desirable to standardize the various sequence valves to some extent, such valves are required to seat and seal at low pressures such as 500 psi, but at the same time the pilot pressure to the system and to all of the valves may increase to a high pressure, such as 3000 psi, which could provide an overstressing of the valve element and valve seat.
The present invention is directed to various improvements in a springless pilot operated sequence valve.